You already know the answer ...; I was saying that a force is just a normal vector, call it magnitude, strength, length, norm, size, whatever you like. The magnitude (strength) is not different from "vector" as Herb said. A vector has a direction and a magnitude (strength).
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Cedric H.Nov 3 '10 at 17:58

In the case of centripetal forces, like gravity, force is always directed towards the center of mass - it's a radial force. We can therefore study most of its properties by calculating its strength.

In particular, with gravity it is typical to use polar coordinates (e.g., in 2D, use angle and radius instead of $x$ and $y$). This leads to a gravitational force which only has a radial component. In this particular case the magnitude of the force vector is the same as the radial component, so it's really easy to calculate.

In the general case, the magnitude is the length of the force vector calculated by the square root of the dot product of the vector by itself. In classical coordinates $(x,y)$

$|F| = \sqrt{(F_x^2 + F_y^2)}$

where $F_x$ and $F_y$ are the $x$ and $y$ components of the force vector ${\bf F}$.